[time-nuts] NCOCXO anyone?

[Charles Steinmetz]

Hal wrote:

> There are 2 markets for DACs and ADCs.  I'll call them DC and RF, but the RF
> goes down to audio.
>
> In the DC market, the data sheet talks about linearity and usually covers
> temperature stability.
>     *     *     *
> In the RF market, nobody cares about temperature drift.

By far the largest market for 16+ bit converters (both ADC and DAC) is 
digital audio.  Virtually all current audio converters use sigma-delta 
("one-bit") conversion with huge oversampling rates.  For a variety of 
reasons, these are quite well suited to the requirements of digital 
audio, but they all have serious shortcomings WRT DC performance, 
tempco, absolute accuracy, and the dreaded idle tones (Google for more 
than you could read in a lifetime).

Fortunately, the sheer volume of this market means that you can get 
really excellent audio (and audio-like) performance for very reasonable 
cost.  Unfortunately, it tempts designers to misuse the inexpensive 
audio chips for general DAQ tasks (for example, the many glorified, 
DC-coupled,  "DAQ" PC sound cards and "instrument on a board" products 
available today).

Best regards,

Charles